This invention is directed generally to apparatus for providing electrical connections, and more particularly to an apparatus for establishing an electrical connection between an electrical bus and a transformer stud.
While this invention may find application in a variety of electro-mechanical connective requirements, the disclosure will be facilitated by specific reference to the problem of establishing optimum electrical and mechanical connection between an underground bus bar connector and a pad mount transformer.
A number of devices have been utilized in the prior art to effect connection of a bus bar to a transformer. Generally a bushing is mounted to the transformer wall which includes a threaded stud that passes through the bushing into the transformer. The stud is used to make connection to wires or conductors within the transformer, and extends outwardly of the transformer to present a threaded surface for connection to external devices. This arrangement then provides an electrical circuit from within the transformer to external cables or the like for electrical distribution. As the use of a bushing and stud of the type described is relatively standarized, it is desirable to provide a method and apparatus for optimizing the electrical and mechanical connection between such a stud and an external device such as a distribution bus.
One approach of the prior art has been to simply provide a threaded hole within the bus and screw the bus onto the transformer stud. Often, a jam nut has been provided on the stud to mechanically lock the bus thereto. It will be recognized that this arrangement does not permit cables to be installed to the distribution bus prior to the installation of the bus to the transformer, as the bus must be rotated to join with the transformer stud. Similarly, if it is desired to remove the bus for any reason, the installed cables thereon must first be removed to permit rotation thereof for removal from the stud.
Another prior art apparatus utilizes an adapter member having a left-handed external thread in combination with a jam nut on the stud. This arrangement requires that the jam nut first be threaded downwardly on the stud, and then the adapter member, which includes a threaded opening, be threaded to a predetermined position on the stud with respect to the jam nut. The distribution bus is provided with an internally threaded receptacle for receiving the exterior thread of the adapter member, such that the adapter member may then be rotated to threadably engage the bus receptacle, and the jam nut threaded back along the transformer stud to mechanically secure the connection. It is apparent that the foregoing presents a relatively cumbersome installation procedure which invites error, especially by a relatively unskilled worker, such that an inadequate electrical and mechanical connection may result. Moreover, it will be noted that in both prior art devices matings between threaded surfaces are relied upon for electrical contact, which is generally less than desirable. Specifically, it is difficult to guarantee sufficient areas of the threaded surface will be maintained in such firm contact as to provide adequate electrical contact surfaces. Moreover, the necessity of providing an internally and externally threaded element as well as a jam nut renders that arrangement relatively expensive.